SALEM - Salem Harbor Station has been shut down in the wake of the deadly steam explosion that killed three workers earlier this week. The power plant, which has 145 employees, could remain closed a week or more, an official said.

Plant owner Dominion said it voluntarily turned off all four of its coal- and oil-fired boilers after the fatal accident Tuesday morning in boiler No. 3. It will take time, the company said, to clean up the area, figure out what went wrong and fix the problem.

"This is not a matter of a couple of days," said Gary Courts, managing director of Dominion New England, which acquired the 745-megawatt Salem plant almost three years ago. "This is going to be some period of time before we can assess what needs to be done."

First-shift employees arrived at the Fort Avenue facility at 7 a.m. yesterday to be told that their co-workers - Mark Mansfield of Peabody, Phillip Robinson of Beverly and Mathew Indeglia of Lawrence - had died overnight at Brigham and Women's Hospital in Boston from severe burns. The company is providing grief counselors, who will be inside the plant for several days.

"This is something that will affect all of us for a long time," Courts said.

The company, which is still paying workers during the shutdown, said it has not been able to inspect the accident scene because of the mess made by the fly ash and other debris that was blown all over the area, and due to initial concerns about asbestos. Subsequent tests, an official said, indicate the air is clean.

Although coal boilers No. 1 and No. 2 were running without incident, the company said it shut everything down "out of an abundance of caution." Boiler No. 4 burns oil and has not been in use recently.

"We really want to take a hard look at the safety of all the units," Courts said.

The fatal accident is being investigated by the Essex County District Attorney's Office, which routinely looks into workplace deaths; the state Department of Public Safety; the federal Occupational Safety and Health Administration; the state Department of Environmental Affairs; and other agencies.

Working on a fan

The company said the employees who were killed were working on a fan a few feet from the boiler and were not working on the boiler itself.

Robinson, 56, a veteran steam operator, was making sure the fan was turned off and safe before Mansfield, 41, a mechanic, began to work on it, the company said. Indeglia, 20, who had been on the job only two days, was watching Robinson to learn about the work of a steam operator, according to company and union officials.

"One thing Dominion does is take a younger person and put them on with our best operator so he can learn from the best," Courts said.

The men were working on the ground floor of the plant when the tube ruptured, blowing steam down on them from 20 feet above, the company said.

A fourth worker had left the area only moments earlier to use the men's room, an official said.

There was no warning that the water tube inside the boiler was about to explode, the company said. No alarms or other warnings sounded in the control room that monitors plant activity.

"There was nothing to indicate there was a problem up until the actual rupture," Courts said.

Inspected in April

The boiler that failed was installed in 1958, the company said. Parts are regularly replaced, but the company did not know the age of the steel tube that ruptured. Courts guessed that it was more than a year old.

State law requires that boilers be inspected annually by a third-party insurance company, and those inspections are certified by the state. Boiler No. 3 was inspected in April, Courts said.

OSHA is not aware of any serious safety problems at the plant. The Salem Fire Department responded to a steam leak in one of the plant's boilers - fire officials could not say which one - in December 2003. That appeared to be a minor incident.

"Dominion shut down the boiler and made repairs," fire Chief Dave Cody said.

Union workers say the plant has a good safety record.

"I can't say enough for the safety program ... in place," said James "Red" Simpson, business manager of the International Brotherhood of Electrical Workers Local 326.

At the same time, however, he acknowledged that work conditions at a power plant that uses hot steam under high pressure are much different than the average workplace.

"This is a very dangerous industry," said Simpson, who used to work at the Salem plant. "This is an extremely dangerous industry."